I know I would have to get two thermometers that read identical to each other. Some wet-bulb set-ups that you can buy that are already put-together have a water reservoir that only holds enough water to barely fill up the cap on a BIC ink pen. If I made my own wet-bulb set-up with two thermometers, and a shoelace, how big of a water reservoir can I use and, not affect the accuracy of the reading? Obviously, I don't want to be always opening the incubator to add water to the wet bulb reservoir. Could I use a reservoir big enough to last the entire incubation period, using a tall narrow container? What distance from the water should the bulb of the "wet" thermometer be? I get the impression from some posts, that humidity is not considered as critically important to maintain at a very specific target as temperature. But, if I am gonna incubate eggs, with the very limited resources that I have, I don't want to be at the mercy of a $5.00 Wal Mart instrument. Yes, I will use an inexpensive digital thermometer/hygrometer but, I will always want to match it's readings to my wet-bulb set-up. That is, if the wet bulb is a very accurate measure of humidity? For the same reason, I will keep several medical thermometers, strategically located throughout the inside of the incubator. Using "rebelcowboysnb" method of confirming the hygrometer's reading would also require me to open the incubator, test it, and then replace the instrument. That salt-testing thing blew me away! Never even heard of such a test before. I'd sure like to get rebelcowboysnb opinion here.